1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to scale having an electronic weighing system and a digital signal processing unit. The electronic weighing system generates a weight-dependent signal, and the digital signal processing unit has circuit or program parts that detect the time elapsed since the connection of a voltage supply to the scale. The time elapsed is used to determine a correction value for correcting the weight-dependent signal.
2. Description of the Related Art
Scales of this type are known, for example, from U.S. Pat. No. 4,763,739. The circuit or program parts that detect the time elapsed since the connection of the voltage supply are used to suppress incorrect weighing results immediately after the voltage supply is connected. Until the voltage supply is connected, all mechanical and electronic components of the scale have the temperature of the scale's environment. However, because the electronic components generate heat during operation of the scale, a certain temperature distribution is gradually established within the scale after the voltage supply is connected and reaches a final steady state after a certain time known as the warm-up time. During this warm-up time, the zero point and/or sensitivity of the scale differs somewhat from the setpoint. As such, there is a risk, particularly in high-resolution scales, that the weighing values will lie outside of specifications. It is therefore customary to suppress the display of the scale during the warm-up time. In U.S. Pat. No. 4,763,739, a fixed duration is provided for the warm-up time.
This fixed duration for the warm-up time must of course correspond to the maximum warm-up time. However, if the scale was only briefly disconnected before the voltage supply was reconnected, the final steady temperature distribution state is reached substantially faster. To take this into account, European Publication EP 1,130,370 proposes a scale in which the digital signal processing unit is provided with computation means to calculate the necessary warm-up time from the signal of a temperature sensor and may also display the calculated warm-up time on the scale's display. As a result, the scale is blocked for the maximum warm-up time only if it has been turned off for a prolonged period of time, whereas if the OFF period was short, the warm-up time is shortened as well. Incidentally, EP 1,130,370 shows a calculated warm-up time of 28 minutes in the exemplary embodiment described there and a possible display of several hours, which makes it clear that the warm-up time may be considerably long in high resolution scales.